In recent decades, bicycle designers have been focusing more and more on the aerodynamic characteristics of bicycles in order to make them faster whilst allowing a cyclist to exert the same amount of effort. Bicycle components, such as frames, wheels and handlebars, to name but a few, have been improving from an aerodynamic point of view at a rapid pace. In more recent years companies have started also to redesign the way bicycle control cables are routed from the control levers to the controlled components.
Control cables are used to control, inter alia, front and back wheel braking mechanisms and front and back shifting mechanisms, such as the front and rear derailleurs. These control cables were conventionally routed directly from the shifters and brakes along the externals of the handlebar, frame and other components without entering the frame or handlebar. However, positioning of these cables outside of the frames has proven troublesome as the cables are exposed to possible damaging conditions. Also, outside mounting of the cables along the tubular frame members sometimes covers art work or graphics on the bicycle frame, thus adversely affecting aesthetic appeal characteristics. Moreover, a bicycle's cables can be held responsible for as much as 3-4% of a bicycle's total aerodynamic losses and such outside mounting of the control cables has a huge adverse effect on a bicycle's aerodynamic performance.
The most aerodynamic method to route a bicycle cable on a bicycle is to do so internally from the control lever to the controlled components. Various attempts have been made in the past to thread or house control cables through bicycle frames. However, such prior art attempts often did not provide for adequate leeway for fluid drainage through the tubes, allowing moisture to enter the tube interior through the openings provided for the cables, thus causing corrosion problems.
One prior art method of routing bicycle cables comprises routing the cables into the bicycle frame on the top and down tube. This system routes the cables along the external of the handlebars and then into the frame via holes in the top tube and down tube of the bicycle. Aerodynamics of this routing method are better than a full external cable routing system, however aerodynamic losses are still evident.
Another prior art method provides routing the cables behind the stem. In particular, the cables are routed along the external handlebars and then into the frame behind the stem. It is currently the most aerodynamically efficient cable routing system, however it still allows for aerodynamic losses from cables being exposed to the wind between the handlebars and frame entry points.
It should be noted that in the above prior art examples the control cables are routed along the handlebar under handlebar tape. The control cables are thus still considered internal for this application until the point where the cable exits from the handlebar tape.
US Patent 2006/0145446 A1 employs a method whereby a hollow steerer tube is used to guide the cables, the steerer tube having two slots at the top end (one at the front and one at the rear) and a flat face on the rear side. This configuration requires a shim in order to stiffen the interface between the fork steerer tube and the upper headset bearing assembly. This system is not as stiff and rigid as a single piece steerer tube. Assembly of the fork and stem is also complex when compared to a single piece steerer tube and this will increase assembly time and cost during service.
Furthermore, the angle through which the handlebar is able to be turned before the cables hinder further rotation is limited when compared to current systems on the market. Such limitation can cause damage to the cables, steerer tube or frame in the event of an accident whereby cables are pinched between the steerer tube and frame. This could result in a failure leading to injury or death if not noticed after such an accident and, since the cables are hidden, such damage may go unnoticed. Such limitation also reduces transport possibilities, such as when handle bars need to be turned rearward when the front wheel is removed and the bicycle is transported between front and rear motor vehicle seats.
The relatively thin walled steerer tube could also cause damage to the cables due to rubbing over the slots of US Patent 2006/0145446 A1.
The hole in the center rear section of the handlebar causes the strength and stiffness to be reduced. As it is in a critical section of the handlebar where stresses are at near maximum levels, it is not an ideal way to route cables into the stem.
US Patent 006983949 B2 makes use of a tubular spacer member with an axial hole for routing in order to route wiring through the upper headset bearing. This method can also be employed to route control cables through the upper headset bearing. However, due to the tight spatial constraints between the outer wall of a conventional steerer tube and the inner wall of the frame's head tube there would in most cases not be sufficient space for such a routing of the control cables. This is especially true for frames that are designed to narrow between the upper and lower headset bearings in order to reduce the frontal area and thus improve the aerodynamic performance of the bicycle. Current Cervelo™ S and P series frames are a good example of this type of narrowing of the head tube.
Furthermore this method requires additional parts and more complex assembly procedures when compared to standard systems.